1. Field of the Invention
This invention relates to a thermoplastic, segmented, linear copolyetherester elastomer having soft segments derived from a poly(alkylene oxide) glycol and hard segments derived from poly(ethylene terephthalate) or poly(butylene terephthalate). More particularly, the invention concerns such elastomers in which the elastomer chains include a small amount of specific difunctional groups, referred to herein as --Q-- units.
2. Description of the Prior Art
Thermoplastic elastomers of segmented, linear copolyetheresters are well known. For example, Shivers, U.S. Pat. No. 3,023,192, among many others, discloses such elastomers composed of long chain ester units which form "soft segments" of the elastomer and short chain ester units which form "hard segments". Among the numerous segments that have been suggested, are soft segments derived from poly(alkylene oxide) glycol (e.g., poly(tetramethylene oxide) glycol, optionally copolymerized with 3-methyltetrahydrofuran) and hard segments of poly(ethylene terephthtalate) and/or poly(1,4-butylene terephthalate). For use in elastic fibers or films, the soft segments usually amount to at least 70 percent of the elastomer weight. Although such elastomers have utility they also have certain shortcomings. For example, such elastomers with hard segments derived from poly(ethylene terephthtalate) are difficult to melt spin into fibers; the elastomer usually crystallizes too slowly and is too tacky to permit satisfactory conversion into fibers or films at commercially viable speeds. Such elastomers with hard segments derived from poly(1,4-butylene terephthtalate) crystallize well, but usually need improvements in elastic properties, particularly in set and unload power. Greene et al, U.S. Pat. No. 4,906,729, discloses some techniques for alleviating these shortcomings. However, further improvements are desirable. An object of this invention is to further improve such copolyetherester elastomers so that they can be converted readily into fibers or films that have a desirable combination of elastic properties.
Though not concerned with copolyetherester elastomers having soft segments derived from a poly(alkylene oxide) glycol and hard segments derived from poly(ethylene terephthtalate) or poly(1,4-butylene terephthtalate), Greene et al, U.S. Pat. Nos. 4,731,435 and 4,810,770, disclose elastomers prepared from certain high molecular weight, relatively rigid, difunctional compounds which amount to 5-25 percent of the elastomer weight. The present inventor has found that by incorporating unusually small quantities of such large difunctional compounds into the elastomers of the present invention, useful improvements are made to the elastomer.